FNB are ******!

I am so sick of this bank! I got a settlement letter and paid off my loan at the beginning of June and yet I’ve had a negative balance and now woke up to a charge for an account that is settled and not in arrears. I have been sent from pillar to post all week trying to get this account closed with no assist and now I have this charge. The agents via the App, email etc. won’t help resolve this issue and I keep being given different answers. I’m tired of FNB and their horrible service. Why would you take money that doesn’t belong to you?